Rosenhan's study was done in two parts. The first part involved the use of healthy associates or "pseudopatients" (three women and five men, including Rosenhan himself) who briefly feigned auditory hallucinations in an attempt to gain admission to 12 different psychiatric hospitals in five different states in various locations in the United States. All were admitted and diagnosed with psychiatric disorders. After admission, the pseudopatients acted normally and told staff that they felt fine and had no longer experienced any additional hallucinations. All were forced to admit to having a mental illness and agree to take antipsychotic drugs as a condition of their release. The average time that the patients spent in the hospital was 19 days. All but one were diagnosed with schizophrenia "in remission" before their release.

This is where it gets funny:

The second part of his study involved an offended hospital administration challenging Rosenhan to send pseudopatients to its facility, whom its staff would then detect. Rosenhan agreed and in the following weeks out of 193 new patients the staff identified 41 as potential pseudopatients, with 19 of these receiving suspicion from at least one psychiatrist and one other staff member. In fact, Rosenhan had sent no one to the hospital.